Dry scrubber system with bacteria

ABSTRACT

Implementations disclosed herein provide a scrubber system for the reduction and removal of acid gas from a gas stream. The scrubber system includes a dry chemical scrubber having an amount of bacteria therein. A gas stream containing an acid gas contaminant such as H 2 S is directed into and treated by the dry chemical scrubber; both media within the scrubber system and bacteria reduce the level of acid gas contaminant in the gas stream. In some implementations, the bacteria is carried over from a biological scrubber fluidly connected upstream of the dry chemical scrubber. The pH of the gas stream from the biological scrubber may be regulated prior to passing into the dry chemical scrubber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/836,547 filed Jun. 18, 2013, and to U.S. Provisional Application No. 61/836,562 filed Jun. 18, 2013, the entire contents of which are incorporated herein by reference for all purposes.

BACKGROUND

Compound gas streams containing acid gases, such as biogas or landfill gas (LFG) streams, can be treated with biological or chemical scrubber systems to remove or reduce the acid components. Recently, suppliers of gas to energy conversion equipment, such as stationery generator sets or gas compression equipment, have tightened allowable limits on acid gas content (e.g., H₂S) in the gas streams reaching this equipment. Additionally, regulatory authorities have imposed more stringent limitations on acid gas concentrations in these or sulfur dioxide (SO₂) emissions from these biogas and LFG conversion processes. Such limitations in turn force lower and sustained limits (often referred to as “bright-line” emission limits) on acid gases, such as H₂S and other sulfur-containing acid gases. These bright-line limits allow no margin for error. As a result, existing biological and chemical scrubber systems are challenged to meet adequate and cost effective performance.

SUMMARY

The present disclosure provides a scrubber system having a biological active (e.g., a bacteria) in a dry chemical scrubber. Implementations of the scrubber system described herein provide enhanced acid gas reduction and removal from gas streams (e.g., biogas or landfill gas (LFG) streams) at a reduced operating cost, compared to a single or multiple biological scrubbers, and compared to a single or multiple dry chemical scrubbers. In some implementation, the scrubber system includes a biological scrubber upstream of a dry chemical scrubber.

In use, a gas stream having acid gas (e.g., hydrogen sulfide (H₂S), hydrogen cyanide (HCN), hydrogen selenide (H₂Se), etc.) is directed into the dry chemical scrubber. Chemicals within the dry chemical scrubber react with the acid gas, thus reducing the acid level in the gas stream. Additionally, in parallel, bacteria within the scrubber consume acid gas to further reduce the amount of the acid gas; the bacteria may be selected specifically for consumption of a particular acid gas, such as sulfur-containing acid gas. In some implementations, a biological scrubber is present upstream of the dry chemical scrubber; a biological scrubber may reduce concentrations of the acid gas by as much as 60-70 percent prior to it entering the dry chemical scrubber. In some implementations, bacteria from the biological scrubber carry over in the gas stream from the biological scrubber to the dry chemical scrubber, replenishing the level of bacteria in the dry chemical scrubber. The implementations disclosed herein can be used to satisfy low level and/or “bright-line” acid gas limits (e.g., industrial equipment limits, warranty limits, utility pipeline limits or regulatory authority restrictions) at a significant operating cost reduction as compared to conventional acid gas treatment systems.

This disclosure provides, in one implementation, a gas treatment system having a biological scrubber system configured to flow a gas stream through a bacteria environment to consume acid gas from the gas stream, and a dry chemical scrubber coupled to an outflow gas stream from the biological scrubber, the dry chemical scrubber including a media to remove acid gas from the outflow gas stream.

This disclosure also provides a gas treatment system comprising a dry chemical scrubber comprising an inlet for an acid gas stream, a reservoir configured to retain media and bacteria therein, the media and the bacteria configured to remove acid gas from the gas stream, a liquid recycle line in fluid communication with the reservoir, and a bacteria inoculation inlet in fluid communication with the reservoir.

This disclosure further provides a method that comprises receiving an input gas stream at a biological scrubber configured to store bacteria to consume acid gas from the input gas stream, and directing an outflow gas stream of the biological scrubber into a dry chemical scrubber configured to hold media that removes acid gas from the output gas stream. The outflow gas stream can have a regulated pH.

This disclosure still further provides a method that comprises directing an acid gas stream into a dry chemical scrubber configured to hold media and bacteria that remove acid gas from the acid gas stream to provide a reduced acid gas stream. The bacteria can be injected into the dry chemical scrubber, for example, via an injection port.

This Summary is provided to introduce an election of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other features, details, utilities, and advantages of the claimed subject matter will be apparent from the following more particular written Detailed Description of various implementations and implementations as further illustrated in the accompanying drawings and defined in the appended claims.

BRIEF DESCRIPTIONS OF THE DRAWINGS

A further understanding of the nature and advantages of the present technology may be realized by reference to the figures, which are described in the remaining portion of the specification.

FIG. 1 is a schematic perspective view of an example dry scrubber system with bacteria therein.

FIG. 2 is a schematic perspective view of an example combined scrubber system.

FIG. 3 is a schematic perspective view of another example combined scrubber system.

FIG. 4 is a diagram of yet another example combined scrubber system.

FIG. 5 is a flow diagram of example operations for gas treatment using a dry scrubber system with bacteria therein.

FIG. 6 is a flow diagram of example operations for gas treatment using a combined scrubber system.

DETAILED DESCRIPTION

Dry chemical scrubbers convert, through chemical reaction, acid gases into other compounds. Dry chemical scrubbers can be engineered to reliably deliver low outlet acid gas concentrations, under a wide range of fluctuating inlet gas conditions. The term “acid gas” is generally used herein to refer to gases that contain chemical elements or compounds of a type such that when the gas is exposed to water or water vapor, an acid is formed; or, that contain water in vapor form that, if condensed, would yield a measured acidic pH, i.e., of less than 7. A “gaseous fluid stream” encompasses gas streams including gas streams with entrained water or other liquid, with the liquid being an aerosol, droplet, particulate, or the like carried by the gas stream. Dry chemical scrubbers, however, due to the reaction with the acid gas, consume chemicals that may need to be replenished over time. Therefore, dry chemical scrubbers are often associated with materially higher operating costs than other systems, such as biological scrubbers.

As used herein, a “dry” chemical scrubber is a chemical scrubber that utilizes a solid media (e.g., iron sponge), rather than a liquid, to present select chemical elements or compounds designed to react with and reduce acid gas in a gas stream. A dry chemical scrubber, in some implementations, does however include liquid components. For example, acid-removal media in a dry chemical scrubber may be moistened by water or other liquid elements that are distributed on or recirculated through the media. This liquid inclusion in a traditional dry chemical scrubber can be for two reasons, to control the temperature of the reaction and to improve the transport mechanism to bring the target acid gas molecules into more immediate and intimate contract with the reactive media. The liquid also affects the environmental conditions within the dry chemical scrubber, for example, to allow biological actives (e.g., bacteria) to thrive within the dry chemical scrubber.

Biological scrubber systems reduce the concentration of acid gases present in an acid gas (e.g., a byproduct gas stream) by treating the gas with a water-based solution that includes a biological active, such as bacteria. Biological scrubber systems require minor amounts of nutrients for bacterial growth, do not consume refractory chemicals and are relatively self-sustaining (e.g., because the bacteria reproduce under properly controlled conditions). However, biological scrubbers do not respond quickly and effectively to fluctuating inlet gas conditions and thus may not reliably meet bright-line acid gas concentration limitations where inlet gas acid concentrations vary during operation (e.g., in biogas and LFG gas streams). And, by their nature biological systems require close control of the operating environment within the biological reactor. Small changes outside that intended environment may result in the death of the bacteria, making the system non-functional for an extended period of time.

The scrubber systems of the present disclosure incorporate the high removal and bright-line performance benefits of a dry chemical scrubber combined with the low cost, possibly high-removal rate associated with bacteria use.

In the following description, reference is made to the accompanying drawing that forms a part hereof and in which are shown by way of illustration at least one specific embodiment. The following description provides additional specific embodiments. In some instances, a reference numeral may have an associated sub-label consisting of a lower-case letter to denote one of multiple similar components. When reference is made to a reference numeral without specification of a sub-label, the reference is intended to refer to all such multiple similar components.

It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided below.

FIG. 1 illustrates an example dry chemical scrubber system 100. The dry scrubber system 100 is a down-flow system having a tank 102 with an internal volume therein; the term “down-flow” and variants thereof means that at least the acid-gas stream flows in a generally downward direction. Present within the tank 102 is media 110 supported by a screen 104. Also present within the tank 102 is an amount of biological active, or bacteria 112; in some implementations, the conditions within the tank 102 (e.g., moisture level, temperature, etc.) are especially conducive to having the bacteria 112 thrive within the tank 102. The bacteria 112 may or may not be homogeneously distributed throughout the media 110.

A first inlet 106 is configured to provide a gas stream 150 (e.g., byproduct gas) into the tank 102 near the top of the tank 102; any number of valves, diverters, baffles or other equipment may be present at or near the inlet 106. A first outlet 108 downstream of the inlet 106 is configured to remove the gas stream, at this stage, as an at least partially de-acidified gas stream 152, from the tank 102.

The tank 102 also includes a second inlet 116 configured to provide a liquid (e.g., water) stream into the tank 102 near the top of the tank 102; any number of valves, diverters, baffles or other equipment may be present at or near the inlet 116. A second outlet 118, downstream of the second inlet 116, is configured to remove the liquid stream from the tank 102. In the particular implementation of system 100, a liquid recirculation or recycle line 117 connects the outlet 118 to the inlet 116. Present in the tank 102, in the recycle line 117, or elsewhere, may be a sump to hold excess liquid, and provide a mechanism for supplying chemical or biological additions to the tank 102. The recycle line 117 or the tank 102 may optionally include a drain to remove excess liquid from the system 100.

In some implementations, a plenum or plenum layer may be present in the dry chemical scrubber 100 downstream of the gas inlet 106. A plenum or plenum layer is a gas distribution layer in fluid communication with the inlet 106 and the media 110; in some implementations, the plenum or plenum layer includes a gas-permeable dividing mechanism such as a baffle plate, or a layer of rock, gravel, or other material having porous passageways that assist in radially dispersing gases across the media 110.

An increasing pressure differential near the top of the tank 102 forces the gas stream 150 down through the media 110 in the tank 102 until it exits the dry scrubber at outlet 108. While moving through the media 110, acidic compounds in the gas stream 150 react with chemicals within the media 110 to at least partially de-acidify the gas and create a non-gas byproduct. In one exemplary implementation, the media 110 is a wood substrate impregnated with iron hydroxide (e.g., an “iron sponge”). In use, the iron hydroxide reacts with hydrogen sulfide (H₂S) and other acids in the gaseous stream to create pyrite or a pyrite-type compound. In other implementations, the media 110 is or includes, without limitation, standard plastic packing, wood chips impregnated with other basic material such as sodium carbonate, sodium bicarbonate, zeolite(s) optionally impregnated or coated with iron and/or oxides, clay coated with iron and/or oxides. As a result of the reaction between the acidic compounds in the gas stream 150 and the media 110, some or all of the acidic compounds are removed from the gas stream 150 to result in gas stream 152.

To increase the removal of acidic compounds from the gas stream 150, the bacteria 112, in some implementations present throughout the media 110, digest the select, especially sulfur bearing, acidic compounds in conjunction with the media 110 reacting with the acid compounds. In some implementations, the conditions (e.g., temperature, pressure, moisture, light level, etc.) within the tank 102 are especially conducive to the growth of the bacteria 112. Depending on the media 110, the media 110 may be particularly conducive to aiding the bacteria 112 to thrive in the tank 102; wood chips, such as those that form an iron sponge, are a suitable nutrient source for the bacteria 112.

The appropriate amount of the bacteria 112 within tank 102 is based on, for example, the concentration of acid gas in the gas stream 150 and the media 110 available to reduce (i.e., react with) the acid gas, the volume flow of the gas stream 150 into the tank 102, the desired concentration of the acid gas, if any, in the output gas stream 152, the conditions (e.g., temperature, moisture, nutrient source, etc.) within the tank 102, and/or the type of bacteria. The specific strains of bacteria 112 utilized may vary based upon the design criteria and desired functionality of the scrubber system 100. Suitable bacteria populations include, without limitation, Thiobacillus thiooxydans, Thiobacillus thioparus, and Thiobacillus intermedius, which can be useful in reducing H₂S to elemental sulfur or oxidizing sulfur, thus removing some portion of the H₂S from the gas stream 150 to provide an acid-reduced gas stream 151. Additional suitable bacteria include those from the genus acidithiobacillus, for example, acidithiobacillus thiooxidans, acidithiobacillus aferrooxidans, acidithiobacillus albertensis, acidithiobacillus caldus, acidithiobacillus cuprithermicus, and acidithiobacillus ferrivorans.

The bacteria 112 digest an amount of the acid gas in gas stream 150, thus further removing some portion of the H₂S from the gas stream 150 to result in a reduced acid gas concentration in gas stream 152. Additionally, the presence of certain bacteria in the tank 102 can accelerate the regeneration of the media 110 (e.g., the iron hydroxide). For instance, the class of bacteria known as “acidophiles” can be utilized as a causative agent for the conversion of iron sulfide compounds into iron oxides and sulfur species such as bisulfides, sulfates, and elemental sulfur. Specifically, the bacteria Acidithiobacillus ferrooxidans aka Thiobacillus ferrooxidans (referred to hereinafter as “acidophile bacteria”) utilizes the conversion of Fe(II) into Fe(III) as an energy source. Therefore, acidophile bacteria may be used in conjunction with certain other ferrooxidans, thiooxidans, sulfidooxidans and oxides to break down triolite absorbed onto spent or partially spent media 110, forming sulfate and elemental sulfur. For example, acidophile bacteria may be added to iron sponge media to react with triolite formed by the reaction between the iron sponge and H₂S. This process leads to the regeneration of iron hydroxide and/or iron oxides, extending the effective life of the iron sponge media.

Additionally, the presence of certain fungal strains may also facilitate the regeneration of the iron hydroxide/oxides and thus extend the operating life of the media 110, especially when in the presence of the above-cited bacteria. For example, the breakdown of the media 110 by the fungal strains may expose a number of new reactive functional sites for the removal of siloxanes and silanols present in the byproduct gas. Such removal occurs through an interaction between the siloxanes and/or silanols and a functional group (i.e., the functional group —CH₂OH) in repeating glucosic molecules in wood chips.

Fungi added to the media 110 work to anaerobically digest the wood chips, providing for regeneration of iron hydroxides and iron oxides and for new functional sites for the removal of siloxanes and solanols. In such a configuration, the media 110 operationally provides for the simultaneous removal of sulfide-containing materials and siloxane/silanol materials from the byproduct gas.

The bacteria 112 can be provided to the tank 102 when the media 110 is packed into the tank 102, however, having an inoculation port 120 allows for continuous or periodic addition of the bacteria 112 into the tank 112 as needed or desired. Although the inoculation port 120 is illustrated feeding directly into the tank 112, other implementations include an inoculation port for depositing the bacteria 112 into a sump or the recycle line 117.

The screen 104 supporting the media 110 and the bacteria 112 may be any suitable porous structure, such as a diffuser plate, gas-permeable cloth, or other media-supporting dividing mechanism. The area below the screen 104 may be an empty containment area or may have any number of possible elements therein, such as baffles, flow directors, additional fluid treatment elements, etc. After the gas stream passes through the media 110, the bacteria 112 and the screen 104, the gas stream exits the tank 102 as the gas stream 152 through the outlet 108 near the base of the tank 102.

In at least one implementation, water is also formed in the reaction between the acidic compounds and the media 110. The water may partially vaporize to form a gaseous product or may remain liquid. Vaporized water exits the tank 102 via the outlet 108 and liquid water exits via the outlet 118; in some implementations, droplets or aerosol of water may be present in the gas stream 152 leaving via the outlet 108.

The dry chemical scrubber system 100 may optionally include one or more sensors or condition-regulator tools such as a pH sensor, temperature sensor or regulator, pressure sensor or regulator, irrigation source, etc. Additionally, the dry chemical scrubber 100 may include a controller (not shown) for actuating valves and pumps that control the flow of the gas into and out of the tank 102. In one implementation, a dehydration unit (not shown) preconditions the gas stream 150 before it enters the tank 102 or before it is distributed within the tank 102.

In some implementations, the media 110 may be mixed with high pH materials such as limestone and soda ash (i.e., calcium and sodium carbonate) before it is placed within the tank 102. Such mix-ins can help to stabilize the pH of the media 110 and associated fluids within the dry chemical scrubber 100. A higher pH at the media 110 results in higher removal of H₂S from the gas stream 150. For example, the solubility of H₂S in water (or in moist media) is greater when the pH is above 7 than if the pH is less than 7. As another example, the solubility of the H₂S at pH 8 is approximately twice the solubility at pH 7. In some implementations, a pH regulator may be included in the scrubber system 100 to regulate and/or adjust the pH of the contents of the tank 102. Examples of pH regulators and their inclusion into dry scrubber systems can be found, for example, in co-pending U.S. patent application Ser. No. ______ (attorney docket number 152015USP), the entire contents of which are incorporated herein by reference for all purposes.

The dry chemical scrubber 100 of FIG. 1 is illustrated as a down-flow system. Alternately, the dry chemical scrubber may be an up-flow system. Both down-flow and up-flow configurations are well known in the field of scrubbers. In a down-flow system, the gas stream (e.g., gas stream 150) enters near the top of the tank (e.g., tank 102) and flows downward under a pressure differential, toward the base of the tank. In an up-flow system, the gas stream (e.g., gas stream 150) enters near the bottom of the tank (e.g., tank 102) and flows upward toward the top of the tank.

FIG. 2 illustrates an example scrubber system having a biological scrubber present as a source of the bacteria for the dry chemical scrubber. In FIG. 2, combined scrubber system 200 has a biological scrubber 210 and a dry chemical scrubber 220 connected in series. Biological scrubber 210 has a tank 212 with an inlet 214 and an outlet 216. Similarly, the dry chemical scrubber 220 has a tank 222 with an inlet 224 and an outlet 226.

An acid-containing gas stream 250 (e.g., containing H₂S) is input through the inlet 214 into the tank 212 of the biological scrubber 210 and exits the tank 212 via the outlet 216 as gas stream 251. This gas stream 251, as gas stream 252, is input through the inlet 224 into the tank 222 of the dry chemical scrubber 220 and exits the tank 222 via the outlet 226 as gas stream 253 having an even further reduced acid content.

The tank 212 of the biological scrubber 210 contains a liquid solution (e.g., a water-based solution) including one or more living strains of bacteria. The specific strains of bacteria utilized may vary based upon the design criteria and desired functionality of the biological scrubber 210. However, suitable bacteria include, without limitation, Thiobacillus thiooxydans, Thiobacillus thioparus, and Thiobacillus intermedius, which can be useful in reducing H₂S to elemental sulfur, thus removing some portion of the H₂S from the gas stream 250 to provide an acid-reduced gas stream 251; the bacteria digest or ‘eat’ an amount of the acid gas in gas stream 250.

To ensure that the bacteria grow and reproduce in the tank 212 during use, certain internal conditions (e.g., pressure, temperature, humidity, pH etc.) of the biological scrubber 210 are maintained within design limits and monitored and/or regulated using one or more sensors (e.g., a pH sensor, a pressure sensor, a temperature sensor) and/or adjusted using one or more regulators (e.g., a temperature regulator, a pressure regulator, a humidity regulator, etc.). Additionally, the biological scrubber 210 may include a controller (not shown) for actuating various valves and pumps that manage the flow of the gas stream 250 into and the flow of the gas stream 251 out of the biological scrubber 210. One or more “bacteria houses” (e.g., structures on which the bacteria can grow) may be positioned within the biological scrubber 210. One or more nets may be used to place such bacteria houses within the biological scrubber 210, and/or to remove the bacteria houses for periodic cleaning. Although the bacteria may be housed or supported on structures, an amount of bacteria is circulating within the tank 212 carried by the gas stream within the tank 212. In some implementations, a useable amount of the bacteria leaves the tank 212 carried by the gas stream 251.

From the outlet 216 of the biological scrubber 210, the gas stream 251 goes to the inlet 226 of the dry chemical scrubber 220 as the gas stream 252. In one implementation, a dehydration unit (not shown), such as a coalescing filter, preconditions the gas stream 251 from the biological scrubber 210 before the stream enters the dry chemical scrubber 220 as gas stream 252.

The dry chemical scrubber 220 is a chemical scrubber that utilizes a media 225 to remove acid gas from the gas stream 252 by reaction. The media 225 includes one or more chemicals (e.g., iron hydroxide) that can be consumed in reactions with the acid gas in the gas stream 252. In one exemplary implementation, the media 225 is iron hydroxide impregnated in a wood substrate (also referred to herein as “iron sponge”) that reacts with hydrogen sulfide in the byproduct gas to create pyrite, or a pyrite-type compound. In other implementations, the media 225 includes, without limitation, standard plastic packing, wood chips impregnated with sodium carbonate, zeolites impregnated with iron oxides, clay impregnated with oxides, and activated carbon such as activated charcoal.

The dry chemical scrubber 220 may include one or more sensors or condition-regulator tools such as a pH sensor, temperature sensor or regulator, pressure sensor or regulator, humidity sensor or regulator, irrigation source, etc. Additionally, the dry chemical scrubber 220 may include a controller (not shown) for actuating valves and pumps that pull the gas into and out of the dry chemical scrubber 220.

As indicated above, some dry chemical scrubbers rely on iron hydroxide to react with acid gases (e.g., H₂S) in the incoming gas stream. Therefore, the consumption rate of the media 225 increases sharply if the pH of the dry chemical scrubber 220 (e.g., gas stream 252) falls below pH 7. Such increased media consumption reduces the effective lifetime of the media 225 and adds significantly to the cost of operation.

In some implementations, the media 225 is mixed with high pH materials such as limestone and soda ash (i.e., calcium and sodium carbonate) before it is placed within the tank 222. Such mixing can help to ensure that the pH of the media and associated fluids does not drop significantly within the dry chemical scrubber 220, thus extending the life of the media 225. Additionally or alternately, increasing the pH value of the gas stream 252 before the gas enters the dry chemical scrubber 220 can further extend the operating life of the media 225.

The biological scrubber 210 and the dry chemical scrubber 220 of the combined system 200 may be separately down-flow scrubbers or up-flow scrubbers; both configurations are well known in the field of scrubbers. In a down-flow system, the gas stream (e.g., gas stream 250 or 252) enters near the top of the tank (e.g., tank 212 or 222) and flows downward under a pressure differential, toward the base of the tank. In an up-flow system, the gas stream (e.g., gas stream 250 or 252) enters near the bottom of the tank (e.g., tank 212 or 222) and flows upward toward the top of the tank.

For an up-flow dry chemical scrubber 220, the scrubber 220 may include a distribution layer and a filtering layer. In such a configuration, the gas stream 252 is fed, via one or more distribution pipes, into the distribution layer where gas is radially distributed in a substantially even manner about the dry chemical scrubber 220. For example, the distribution layer may be a layer of loose gravel or rock fragments that distribute the gas by forcing it to spread out through a number of porous, narrow pathways. Alternatively, the distribution layer may be a diffuser plate supported above an air plenum layer. The diffuser plate may have holes sized and spaced to provide for a controlled pressure drop across the plate.

In one implementation of the combined system 200, the biological scrubber 210 reduces the concentration of acid gas by approximately 75% of an initial concentration of the gas stream 250, and the dry chemical scrubber 220 reduces the concentration of acid gas from gas stream 252 to a target bright-line outlet condition. Thus, a total acid gas reduction yielded, from gas stream 250 to gas stream 253, can be as much as 95+%. Having bacteria from the biological scrubber 210 flow over into the dry chemical scrubber 220 extends the working life of the media 225, thus extending the life of the combined system 200 and reducing its operating cost.

FIG. 3 illustrates another example combined scrubber system 300 having a biological scrubber 310 and a dry chemical scrubber 320 connected in series. The biological scrubber 310 has a tank 312 with an inlet 314 and an outlet 316. Similarly, the dry chemical scrubber 320 has a tank 322 with an inlet 324 and an outlet 326. The combined system 300 further includes a pH regulator 330 fluidly connected between the biological scrubber 310 and the dry chemical scrubber 320.

An acid-containing gas stream 350 (e.g., containing H₂S) is input through the inlet 314 into the tank 312 of the biological scrubber 310 and exits the tank 312 via the outlet 316 as gas stream 351, having a reduced acid content and optionally an amount of bacteria therein. The gas stream 351 passes through the pH regulator 330 and the result is gas stream 352, which is input through the inlet 324 into the tank 322 of the dry chemical scrubber 320 and exits the tank 322 via the outlet 326 as gas stream 353 having an even further reduced acid content.

Similar to the biological scrubber 210 of combined system 200, the tank 312 of the biological scrubber 310 of combined system 300 contains a liquid solution (e.g., a water-based solution) including one or more living strains of bacteria. The specific strains of bacteria utilized may vary based upon the design criteria and desired functionality of the biological scrubber 210. The bacteria ‘eat’ at least an amount of the acid gas in gas stream 350.

At least in this implementation, the biological scrubber 310 operates at a low pH (e.g., below pH 7) and gas stream 351 outbound from the biological scrubber 310 may thus contain liquids, gases, or solids that have a pH below pH 7. Inputting the gas stream 351 at this low pH into the dry chemical scrubber 320 may result in degraded performance (e.g., increased media consumption) of the dry chemical scrubber 320, which could at least partially offset or negate the positive effect of including both the biological scrubber 310 and the dry chemical scrubber 320 within the combined scrubber system 300. Therefore, the gas stream 351 outbound from the biological scrubber 320 (e.g., through the outlet 316) is subjected to a pH adjustment via the pH regulator 330 prior to passing through the inlet 324 into the dry chemical scrubber 320. The pH regulator 330 increases the pH of the gas stream 351 to a level compatible with internal operating conditions of the dry chemical scrubber 320. Although the specific degree of such pH adjustment may vary, the pH of the outgoing gas stream 352 from the pH regulator 330 is, in several implementations, at or above pH 7. In one implementation, the pH of outgoing gas from the pH regulator 330 is at or between pH 8 and pH 10.

The pH regulator 330 includes high pH elements that contact the gas stream 351 to raise the pH of the resulting gas stream 352 to within a predetermined pH range before the gas stream 352 passes into the dry chemical scrubber 320. The high pH elements may be in liquid, solid, or gas form.

The pH regulator 330 can include a pH sensor, various valves and injectors, etc. to monitor the pH of the gas stream 351 and increase the pH when needed. The gas stream 351 may be passed through an internal environment of the pH regulator 330 including the high pH materials. In one example implementation, the high pH materials (e.g., calcium carbonate) are included in an aqueous solution through which the gas stream 351 is directed. For example, the high pH materials may be included in an aqueous solution, and a bleed line under a slight positive pressure may pull the aqueous solution into contact with the gas stream 351. The aqueous solution may be fed, for example, into a pipe containing the gas stream 351. In another example implementation, the high pH materials are in a vapor or mist injected into the gas stream 351.

In still another example implementation, the gas stream 351 is passed through a bed of particulate high pH materials, such as calcium carbonate. In another implementation, the pH regulator 330 is a column packed with inert material into or onto which the high pH materials are drawn, coated or injected. In one implementation, the gas stream 351 flows up through the packed column while an aqueous solution containing high pH materials flows down through the column. The high pH materials may be continuously or periodically added to the gas stream 351 before the gas passes into the dry chemical scrubber 320.

The pH regulator 330, in some implementations, is a passive system, automatically adjusting the pH of the gas stream flowing through the pH regulator 330. A passive system adjusts the pH level of the gas stream without interaction or input by a person (e.g., an operator); no sensors, valves, regulators, diverters, etc. are needed to control the flow of the gas through the pH regulator 330 nor to activate or deactivate the pH regulator 330. The pH regulator 330 functions on a pH equilibrium theory, with the pH regulator 330 automatically adjusting the pH level of the gas flowing through it, if needed. As an example, if the high pH materials in pH regulator 330 have a pH of 10, and if the initial pH of the gas passing through the pH regulator 330 is less than 10, the high pH materials in regulator 330 will raise the pH of the gas to above the initial pH, but less than 10, as the gas passes through the pH regulator 330. If the initial pH of the gas passing through the pH regulator 330 is at or greater than 10, the high pH elements in regulator 330 will not raise the pH of the gas. It should be understood that the pH level of the gas may not be raised as high as the pH of the high pH materials, but the pH level of the gas will be raised as the gas passes through the pH regulator 330.

Other implementations of pH regulators for scrubber systems are described in co-pending U.S. patent application Ser. No. ______ (attorney docket number 152015USP).

In some implementations, the combined system 300 may include pH monitoring of, for example, the gas stream 351, the gas stream 352, of the contents in the tank 322, etc., which can be used to affect the pH regulator 330 and its adjustment or regulation of the pH of the gas stream.

From the pH regulator 330, the gas stream 352, having a pH of 7 or greater, enters the dry chemical scrubber 320 via the inlet 324. Similar to the dry chemical scrubber 120 of combined system 100, the dry chemical scrubber 320 is a chemical scrubber that utilizes a media 325 (e.g., iron sponge, zeolites, coated clay granules, etc.) to remove acid gas from the gas stream 352 by reaction. The media 325 includes one or more chemicals (e.g., iron hydroxide) that can be consumed in reactions with the acid gas in the gas stream 352. Because the consumption rate of the media 325 increases sharply if the pH of the dry chemical scrubber 320 (e.g., gas stream 352) falls below pH 7, including the pH regulator 330 upstream of the dry chemical scrubber 320 extends the effective lifetime of the media 325 and reduces the cost of operation. Optionally present in the dry chemical scrubber 320 is bacteria to eat acid gas from the gas stream 352.

The resulting output gas stream 353 from the outlet 326 has a greatly reduced acid gas concentration compared to the input gas stream 350. In one implementation, the biological scrubber 310 reduces the concentration of acid gas by approximately 75% of an initial concentration, and the dry chemical scrubber 320 reduces the concentration of acid gas to a target bright-line outlet condition. Thus, a total acid gas reduction, from gas stream 350 to gas stream 353, can be as much as 99+%.

For both or either combined scrubber systems 200 and 300, various performance metrics may be attained according to desired design criteria. In one example implementation, the combined scrubber system 200, 300 reduces the concentration of H₂S in an incoming gas stream to a final gas stream having a concentration of at or below 3 ppm (e.g., to prevent corrosion of piping and/or possible leaks or explosions in utility pipelines). In another example implementation, the incoming gas stream 250, 350 is a biogas fuel supply stream and the combined scrubber system 200, 300 reduces the concentration of H₂S to at or below 5 ppm. In yet another example implementation the gas stream 250, 350 is a biogas fuel supply stream and the combined scrubber system 200, 300 reduces the concentration of H₂S in the gas stream 253, 353 to at or below 50 ppm. In still yet another implementation, the combined scrubber system 200, 300 reduces the concentration of H₂S in the gas stream 250, 350 to at or below 200 ppm. In another implementation, the combined scrubber system 200, 300 reduces the concentration of H₂S in the gas stream 250, 350 to at or below 400 ppm.

FIG. 4 illustrates another example combined scrubber system 400 including a biological scrubber 410 fluidly connected to a dry chemical scrubber 420. The biological scrubber 410 includes a reaction vessel or tank 412 connected to a bio sump 415 by way of a water return line 419. Liquid (e.g., water) in the bio sump 415 is heated by a heating fluid loop 413 to a temperature suitable for growth and support of bacteria contained within the reaction vessel 412.

A blower 414 blows air into the bio sump 415 to aerate the bio sump 415, while a pump 418 draws liquid, optionally enriched via a nutrient source, up through a water line inlet and through an input line 419 of the reaction vessel 412. A gas stream 450 is fed to the reaction vessel 412 via an inlet gas line. Within the reaction vessel 412, bacteria consume quantities of one or more acid gases in the incoming gas stream 450, reducing the concentration of acid gas in the gas stream. The liquid within the reaction vessel 412 is permitted to drain, via the water return line 416, into the bio sump 415. The liquid in the bio sump 315 may be diluted with fresh water, re-enriched with nutrients and/or reheated prior to recirculation through the reaction vessel 412.

The gas stream, having been reduced in acid gas levels and optionally including some of the nutrients from vessel 412, exits the reaction vessel 412 via an outlet gas line as stream 451. The outlet gas stream 451 is routed from the reaction vessel 412 into a pH regulator 430, which includes a high pH buffer solution (i.e., with a pH at or above 7). When the gas stream is passed through the high pH buffer solution, the pH of the gas stream is increased to a level compatible with input requirements of the dry chemical scrubber 420. Some of the high pH buffer solution within the pH regulator 430 is permitted to drain, via a buffer return line 434, into a buffer sump 435. The solution in the buffer sump 435 is recycled through the pH regulator 430 through a buffer solution input line 434. In one implementation, the buffer sump 435 is monitored and chemicals are added as necessary to maintain the pH of the solution therein. The buffer solution may include a variety of high-pH materials, including without limitation, calcium, sodium carbonate, sodium hydroxide, ammonia, etc.

A blower 436 draws the pH-adjusted gas stream out of the pH regulator 430 through an output gas line 452, and the pH-adjusted gas stream is directed into a tank 422 of the dry chemical scrubber system 420. The dry chemical scrubber 422 includes the tank 422, a water line 424, and a chemical scrubber sump 425. The tank 422 is connected to the chemical scrubber sump 425 by way of a water return line 426. In one implementation, the pH-adjusted gas stream is dried by a drying mechanism (not shown) just before or after the pH-adjusted gas enters the tank 422 of the dry chemical scrubber 420. Water can be added to the tank 422 via the water line 424 (e.g., an irrigation system). The water drains from the tank 422 through the water return line 426 into the chemical scrubber sump 425, and is recycled from the chemical scrubber sump 425 to the water line 424.

In another implementation, the combined scrubber system 400 does not include the pH regulator 430 and the buffer sump 435. Rather, high pH elements are added to the water that moistens the media present in the tank 422; this water may be fresh water or recycled (e.g., water from the chemical scrubber sump 425 or elsewhere). U.S. patent application Ser. No. ______ (attorney docket 152015USP) provides various implementations of using high pH elements in a water line to adjust the pH within a dry chemical scrubber.

In FIG. 4, the dry chemical scrubber 420 is a down-flow system wherein the pH-adjusted gas flows from the top of the tank 422 to the bottom of the tank 422. Thus, the tank 422 may be an airtight vessel. Building pressure of the pH-adjusted gas near the top of the tank 422 forces the gas down through a media in the tank 422 and toward an outlet for the treated gas stream 453. The media in the tank 422 reacts with one or more acid gases in the pH-adjusted gas stream, reducing the concentration of acid gas present in the pH-adjusted gas stream.

In another implementation, the dry chemical scrubber 420 is an up-flow system. The pH-adjusted gas stream is input to the tank 422 through a port near the base of the tank 422, and the gas stream rises throughout the tank 422 and exits the tank 422 through a valve or other opening proximal to the top of the tank 422. In such an up-flow system, the tank 422 may or may not be airtight.

FIG. 5 illustrates example operations for removing acid gas from a gas stream using a dry chemical scrubber system having bacteria therein. A providing operation 502 provides, to a dry chemical scrubber, a source of bacteria; the source may be, for example, bacteria inoculated into the dry chemical scrubber tank, or bacteria carried over from an upstream process. The dry chemical scrubber is configured to store bacteria to consume acid gas from the input gas stream in addition to having a media that reacts with the acid gas. The dry chemical scrubber may operate at a high or a low pH value and have one or more internal conditions (e.g., temperature, moisture, pressure) that are monitored and/or regulated to ensure the health of the bacteria. An acid gas stream is passed into and through the dry chemical scrubber in operation 506. In addition to the bacteria in the dry chemical scrubber, the dry chemical scrubber can have media that includes chemicals that react with acid gas in the gas stream, thus removing additional acid gas from the gas stream.

An optional adjusting operation 504 preconditions the acid gas stream prior to its passing through the dry chemical scrubber. In one implementation, the adjusting operation 504 adjusts a pH of the gas stream before the gas stream enters the dry chemical scrubber. According to another implementation, the adjusting operation 504 adjusts a pH of the gas stream after the gas stream enters the dry chemical scrubber. For example, the dry chemical scrubber may include a pH regulator that is part of an irrigation system that moistens media within the dry chemical scrubber.

FIG. 6 illustrates example operations for removing acid gas from a gas stream using an example combined scrubber system. A receiving operation 602 receives, at a biological scrubber, an input gas stream. The biological scrubber includes a reservoir and is configured to store bacteria to consume acid gas from the input gas stream. The biological scrubber may operate at a high or a low pH value and have one or more internal conditions (e.g., temperature, moisture, pressure) that are monitored and/or regulated to ensure the health of the bacteria.

An optional preconditioning operation 604 preconditions an outflow gas stream of the biological scrubber. The preconditioning operation 604 may precondition the outflow gas stream before or after it enters a dry chemical scrubber. In one implementation, the preconditioning operation 604 adjusts a pH of the outflow gas stream before the outflow gas stream enters the dry chemical scrubber. According to another implementation, the preconditioning operation 604 adjusts a pH of the outflow gas stream after the outflow gas stream enters the dry chemical scrubber. For example, the dry chemical scrubber may include a pH regulator that is part of an irrigation system that moistens media within the dry chemical scrubber.

A directing operation 606 directs the preconditioned outflow gas stream of the biological scrubber into media within the dry chemical scrubber. The media may include chemicals that react with acid gas in the outflow gas stream to produce a non-gas byproduct, thus removing additional acid gas from the gas stream.

The above specification, examples, and drawings provide a complete description of the structure and use of exemplary implementations of the invention. Since many implementations of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. It is understood that the features of any of the implementations discussed above may be rearranged without departing from the spirit and scope of the invention. Furthermore, structural features of the different implementations may be combined in yet another implementation without departing from the recited claims. 

What is claimed is:
 1. A dry chemical scrubber system comprising: an inlet for an acid gas stream, a reservoir configured to retain media and bacteria therein, the media and the bacteria configured to remove acid gas from the gas stream, a liquid recycle line in fluid communication with the reservoir, and a bacteria inoculation inlet in fluid communication with the reservoir.
 2. The dry chemical scrubber system of claim 1, wherein the acid gas is H₂S and the bacteria comprises Thiobacillus thiooxydans, Thiobacillus thioparus, or Thiobacillus intermedius.
 3. The dry chemical scrubber system of claim 1, wherein the acid gas is H₂S and the media comprises an iron sponge.
 4. The dry chemical scrubber system of claim 1, wherein the bacteria inoculation inlet is into the reservoir.
 5. The dry chemical scrubber system of claim 1, wherein the bacteria inoculation inlet is into the liquid recycle line.
 6. The dry chemical scrubber system of claim 1, further comprising a pH regulator that regulates a pH value within the dry chemical scrubber.
 7. The dry chemical scrubber system of claim 6, wherein the pH regulator is present in the liquid recycle line.
 8. A gas treatment system comprising: a biological scrubber system configured to flow a gas stream through a bacteria environment to consume acid gas from the gas stream; and a dry chemical scrubber coupled to an outflow gas stream from the biological scrubber, the dry chemical scrubber including a media to remove acid gas from the outflow gas stream.
 9. The gas treatment system of claim 8, wherein the dry chemical scrubber is a pH-regulated dry chemical scrubber configured to adjust an internal pH value of the dry chemical scrubber.
 10. The gas treatment system of claim 9, further comprising a pH regulator fluidly connected in the outflow gas stream between the biological scrubber and the dry chemical scrubber.
 11. The gas treatment system of claim 9, further comprising a pH regulator present in a liquid input line to the dry chemical scrubber.
 12. The gas treatment system of claim 8, further comprising one or more nets to position bacteria houses within the biological scrubber.
 13. The gas treatment system of claim 8, wherein the media in the dry chemical scrubber comprises an iron sponge.
 14. The gas treatment system of claim 13, the dry chemical scrubber configured to retain bacteria therein.
 15. A method comprising: receiving an input gas stream at a biological scrubber configured to store bacteria to consume acid gas from the input gas stream; and directing an outflow gas stream of the biological scrubber into a dry chemical scrubber configured to hold media and bacteria that remove acid gas from the output gas stream.
 16. The method of claim 15, further comprising: directing the outflow gas stream through a pH regulator external to the dry chemical scrubber, wherein the pH regulator regulates the pH value of the outflow gas stream entering the dry chemical scrubber.
 17. The method of claim 15, wherein the outflow gas stream comprises bacteria from the biological scrubber.
 18. The method of claim 17, wherein the outflow gas stream comprises H₂S and Thiobacillus thiooxydans, Thiobacillus thioparus, or Thiobacillus intermedius.
 19. A method comprising: injecting bacteria into a dry chemical scrubber configured to hold media and bacteria that remove acid gas from an acid gas stream to provide a reduced acid gas stream; and directing an acid gas stream into the dry chemical scrubber.
 20. The method of claim 19, wherein the acid gas comprises H₂S and the bacteria comprises Thiobacillus thiooxydans, Thiobacillus thioparus, or Thiobacillus intermedius. 